1. Field of the Invention
This invention relates generally to arc welders which include means for reducing the open circuit voltage (OCV) when welding is not actually occurring and, more particularly, to such a power supply having an improved voltage reducing means including a fail-safe circuit which interrupts the power supply if the voltage-reducing circuit should not operate properly.
2. Description of the Prior Art
When utilizing certain types of electric power supplies for paticular arc welding applications, there exists a potential operator hazard due to the magnitude of voltage normally present at the output terminals of the power supply. Power supplies used for stick welding may have output voltages up to 80VAC (RMS) with no contactor or other means of removing this voltage from the output terminals when a weld is not actually being made. Under normal circumstances where the welder is dry and the operator can stay out of contact with the workpiece, the problem has been relatively small. However, under wet conditions and/or in confined spaces, the continuous presence of the relatively high open circuit voltage (OCV) can present a safety problem which is recognized by current federal regulations and industry standards.
Voltage reducers for arc welders are broadly known. For example, U.S. Pat. No. 2,775,735 discloses an automatic voltage reducing circuit employing a voltage divider and relays for automatically reducing the no-load voltage when the arc is interrupted and not restruck within a predetermined minimum time period; this circuit does not contain a fail-safe function. U.S. Pat. No. 4,151,396 discloses a safety system which includes an automatically controlled switch prevents uncontrolled open circuit voltage from existing at the electrode holder when the welding arc is interrupted; however, there is no time delay or fail-safe function.